WORK-UP OF GASTROINTESTINAL MICROSPORIDIOSIS

Microsporidia, which are members of the phylum Microspora, are increas ingly recognized as causing opportunistic infections in persons with i mmunodeficiency (e.g., AIDS). Diarrhea is the predominant clinical sig n associated with infections by two Microsporidia, namely Enterocytozo on bieneusi and Encephalitozoon intestinalis (which was formerly named Septata intestinalis). Prevalence rates of microsporidiosis in person s with AIDS and chronic diarrhea range fron 7 to 50%. Transmission ele ctron microscopy has been the gold standard by which to diagnose micro sporidiosis and requires observing a polar filament which is the struc ture distinguishing Microsporidia from other organisms. Transmission e lectron microscopy is difficult, time-consuming, costly, relatively in sensitive, and requires a great deal of expertise. As such, histochemi cal methods have been developed and improved for detecting Microsporid ia. Diagnoses from stool specimens or enteric fluids can be made using the chitin-staining fluorochromes (e.g., Calcofluor White) and the mo dified trichrome stain which are highly sensitive, particularly when b oth are used. Immunofluorescent antibody staining methods are being de veloped to improve specificity, but reagents are not yet commercially available. Microsporidia can be detected most readily in tissue biopsi es by Gram stain, Giemsa stain, or immunofluorescent antibody. Polymer ase chain reaction methods are in their infancy for application, but s hould prove to be particularly sensitive and specific in the future.